Solvay declined as much as 4.68 euros, or 5.5 percent, to 80.60 euros, the steepest drop since November 2005. The stock fell 3.23 euros, or 3.8 percent, to 82.05 euros at 10:39 a.m. local time. They've declined 14 percent this year.

Wyeth, based in Madison, New Jersey, said today it would hand back rights to the bifeprunox experimental antipsychotic therapy and other compounds. Brussels-based Solvay slashed its forecast for drug sales in September after failing to win U.S. approval for bifeprunox. The Food and Drug Administration asked Solvay and Wyeth to do more tests before the agency would consider approving the medicine.

Hanssens cut his price target on Solvay by 2 euros to 102 euros, and kept a "hold'' rating on the stock. Rabo Securities also cut its price target on Solvay by 2 euros to 88 euros and maintained a "hold'' rating on Solvay, the company said in a note to investors today.

Solvay will "analyze all options'' for the compounds to which Wyeth relinquished its rights, Executive Vice President Claus Steinborn said in an e-mailed statement today.

Solvay is now under pressure to present successful results from late-phase trials on an updated version of its fenofibrate cholesterol medication, which it's developing with Abbott Laboratories, Hanssen said. The results are scheduled to be presented at the American College of Cardiology's conference beginning March 29 in Chicago, he said.

Solvay has changed radically in recent years, into a group focused on competitiveness, leadership and high added value activities, aimed at sustained and profitable growth and led by a passion for innovation. Solvay, which operates in Pharmaceuticals, Chemicals and Plastics, generated EUR 9.6 billion of sales in 2007 from more than 400 units in over 50 countries. Some 28,300 people apply their talents daily to satisfying the demands of the Group’s 160 000 clients.

Wyeth is known for manufacturing the over-the-counter drugs Robitussin and the analgesic Advil, as well as the prescription drugs Premarin and Effexor, which both boast over $3 billion in sales annually.